1. Field of the Invention
This invention relates to a toner for use in image-forming methods that utilize electrophotographic, electrostatic recording and toner jet recording technologies.
2. Description of the Related Art
In recent years, energy savings has been a major technical concern even in image-forming apparatuses such as electrophotographic equipment. There is, in particular, a desire for a reduction in the quantity of heat consumed by the fixing apparatus. Hence the growing need to enhance the quality referred to as “low-temperature fixability” that enables fixing to occur with the expenditure of less energy.
To enable fixing to occur at a lower temperature, one approach hitherto known to be effective is to have the binder resin included in the toner be sharp-melting. Toners which use crystalline polyester resin have been introduced as one such type of toner. Crystalline polyester resins, owing to the regular arrangement of the molecular chain, have certain characteristics: they do not exhibit a clear glass transition, are resistant to softening at temperatures below the crystal melting point, and rapidly soften above the crystal melting point. Hence, they are being studied as materials capable of providing both heat-resistant storage stability and a low-temperature fixability.
Japanese Patent Application Laid-open No. S62-47649 describes art that achieves both heat-resistant storage stability and low-temperature fixability by using as the binder a copolymer obtained by bonding crystalline polyester blocks with amorphous polyester blocks.
Japanese Patent No. 4571975 discloses art that achieves both low-temperature fixability and offset resistance by using together, as the binder resin, both a copolymer of a crystalline polyester resin with an amorphous styrene-acrylic resin, and also an amorphous styrene-acrylic resin.
Japanese Patent Application Laid-open No. 2010-168529 teaches art which achieves both heat-resistant storage stability and good melting properties by using a resin composed of crystalline segments in which an aliphatic polyester serves as an essential component, bonded with amorphous segments.
At the same time, there also exists a desire to enhance the stability of the image quality when storing images that have been output. In cases where the toner has a low strength, when the output image is rubbed by outside forces or the image itself is folded, toner is sometimes shed at the rubbed or folded areas.
Also, the toner incurs various impacts within electrophotographic equipment. For example, it incurs impacts due to the feed screws and pressure by the regulating blades within the developing device, and also incurs pressure at the blades within the cleaning device. When toner breakage and chipping arises due to such impacts, contamination of the regulating blade and filming on the photoreceptor owing to the fine powder generated as a result tend to give rise to image defects such as streaks and blank dots on the image.
Moreover, the cleaning work and parts replacement work that arise in connection with toner clogging in the cleaning zone, and the increased frequency of photoreceptor replacement associated with wear detract from the maintenance-free features of the equipment.
However, in crystalline resins, the strength of the resin itself is generally low compared with that of amorphous resins, which poses a problem in terms of the reliability of the powder. Even the above toners which use a block polymer obtained by bonding a crystalline resin with an amorphous resin have not always been able to fully address such needs.
Japanese Patent No. 4544095 describes a toner composed of a core made of a block polymer of crystalline polyester and amorphous polyester, and an amorphous polyester shell covering the core. Although this method does enable filming on the photoreceptor to be prevented to some degree, it leaves something to be desired from the standpoint of preventing breakage and chipping of the toner and enhancing toner durability over a longer period of time.
Toners that are capable of resolving the above problems have not previously been achieved, and so there has remained a desire for a toner having a higher durability.